1. Field of the Invention
The present invention relates to generally to silicone compositions that are useful for controlling foam formation in foaming media. More particularly, the present invention relates to such antifoam compositions in the form of an emulsion, wherein a discontinuous silicone phase is dispersed in a nonpolar organic continuous phase.
2. Description of the Prior Art
Silicone compositions, useful as foam control agents and which are prepared by a reaction of several components, have been disclosed. For example, Aizawa et al., in U.S. Pat. Nos. 4,639,489 and 4,749,740, teach a method for producing a silicone defoamer composition wherein a complex mixture of polyorganosiloxanes, filler, a resinous siloxane and a catalyst are heated together at 50.degree. C. to 300.degree. C. The drawback of the compositions of Aizawa et al. is that the cost to manufacture the composition is quite high.
Terae et al., in U.S. Pat. No. 4,690,713, disclose an antifoam composition comprising (a) 100 parts by weight of a hydrocarbon oil, such as a spindle oil or silicone fluid (e.g. a polydimethylsiloxane fluid having a viscosity of 20 to 1,000,000 mm.sup.2 /sec at 25.degree. C.), (b) 0.1 to 40 parts by weight of an organosilane compound having 1 to 3 hydroxy groups or hydrolyzable groups (such as alkoxy, acyloxy, and alkenyloxy groups), and(c) 1 to 40 parts by weight of a finely divided silica powder and optionally a catalyst.
Starch, in U.S. Pat. No. 4,983,316 discloses a dispersible antifoam composition for providing controlled foaming liquid laundry detergent formulations, wherein there is provided a non-aqueous emulsion of primary and secondary silicone antifoam agents, at least one nonionic silicone surfactant for emulsifying the primary and secondary antifoaming agents in a solvent, a first organic surfactant dispersing agent for assisting in dispersing the emulsified primary and secondary antifoaming agents in the liquid laundry detergents, and a second dispersing agent of a nonionic difunctional block-copolymer terminating in primary hydroxyl groups for further assisting in dispersing the emulsified primary and secondary antifoam agents in the liquid laundry detergent. A liquid laundry detergent composition containing the composition described immediately above is also disclosed. A drawback of this composition is the high cost associated with manufacture. Another drawback is that the active antifoam agent needs to be diluted for stability and delivery to the foaming medium. Such dilution causes the performance to suffer proportionately.
Silicone compositions which contain polybutylene or polyisobutylene compounds have also been disclosed. For example, Smith et al. in U.S. Pat. No. 3,959,175 discloses a defoamer based on a mixture of polyisobutylene and a high melting point hydrophobic component such as a fatty amide, fatty acid, or tri-glyceride, a mixture of the polyisobutylene and a hydrophobic material such as treated silica powder, or a combination of the two mixtures. It is well-known that antifoam agents of this type, however, do not offer the long-term performance seen in silicone-based antifoam agents.